Kit Mods & Safety & Awesomeness

General info from SeeMeCNC HQ
User avatar
geneb
ULTIMATE 3D JEDDI
Posts: 4742
Joined: Mon Oct 15, 2012 12:47 pm
Location: Graham, WA
Contact:

Re: Kit Mods & Safety & Awesomeness

Postby geneb » Fri Oct 02, 2015 12:10 pm

Holy1, that won't help if the FET that drives the hot end has failed. They tend to fail "on", meaning they'll deliver the full output of the power supply to the hot end or heated bed. The only thing the controller can do in that instance is to open a relay that's feeding power to the FET.

g.
Delta Power!
Defeat the Cartesian Agenda!
http://www.f15sim.com - 80-0007, The only one of its kind.
http://geneb.simpits.org - Technical and Simulator Projects

Holy1
Printmaster!
Posts: 349
Joined: Fri Jan 24, 2014 12:53 pm

Re: Kit Mods & Safety & Awesomeness

Postby Holy1 » Fri Oct 02, 2015 12:44 pm

Ok, I guess I wasn't considering the full worst case scenario. I'll be quiet now :roll:
Orion to Cartesian viewtopic.php?f=59&t=7808

cope413
Printmaster!
Posts: 446
Joined: Sun Jun 30, 2013 5:52 pm
Location: Orange County, CA
Contact:

Re: Kit Mods & Safety & Awesomeness

Postby cope413 » Fri Oct 02, 2015 12:56 pm

johnoly99 wrote: but also remember, copes pics could be much MUCH worse had he not caught them in time before they fell on to the carpet :o


Oh cmon, aluminum only melts around 1200F. Pretty sure my carpet could handle well over 1400F.
Fellow Philosophy majors unite!

"The proverbial achilles heel of property monistic epiphenomenalism is the apparent impossibility of ex-nihilo materialization of non-structural and qualitatively new causal powers."

User avatar
Jimustanguitar
ULTIMATE 3D JEDDI
Posts: 2631
Joined: Sun Mar 31, 2013 1:35 am
Location: Notre Dame area
Contact:

Re: Kit Mods & Safety & Awesomeness

Postby Jimustanguitar » Fri Oct 02, 2015 2:03 pm

The problem with software solutions, even firmware, is that they are still computers. There are glitches, things freeze, and it's not impossible for things to go wrong. In my opinion, the best protection from runaway in a heater that won't self destruct (i.e. a ceramic cartridge) is a thermal cutoff "fuse" like others have linked in this thread. That's not to say that software wouldn't reduce incidents, it certainly would, but it's a failsafe that can also fail. Use both - redundant safety is a good thing.

Even if you don't have a runaway heater, normal printing temperatures can exceed the Bradbury point.
Image
There is a level of danger at play even when things don't go awry. If you have paper around your printer, foam glued in your enclosure, etc there's always some way that final destination can fulfill its destiny. The universe it built on entropy, after all.


Regardless of the gear that you use or how safe or unsafe it may potentially be, be aware of what you're doing. Understand the machine and know the dangers involved. It's all about awareness, and that's what Steve was getting at. That's the message that I read.

Print safe, guys!

User avatar
PartDaddy
Printmaster!
Posts: 345
Joined: Fri Mar 23, 2012 4:03 pm

Re: Kit Mods & Safety & Awesomeness

Postby PartDaddy » Fri Oct 02, 2015 2:45 pm

And, when you are aware of everything, it can still bite you anyway.

Now we have this under control, let's all design Oly's idea for a hot end heated by open flame.
~PartDaddy
SeeMeCNC Owner & Founder
Blackpoint Engineering is SeeMeCNC
Since 1996

Polygonhell
ULTIMATE 3D JEDDI
Posts: 2430
Joined: Mon Mar 26, 2012 1:44 pm
Location: Redmond WA

Re: Kit Mods & Safety & Awesomeness

Postby Polygonhell » Fri Oct 02, 2015 4:22 pm

Holy1 wrote:I am using the repetier 92.3 version that has the watchdog feature. If there was a runaway situation it simply decouples the power to the hotend. I tested it by pulling out the thermistor when it up to temp and sure enough it worked fine, powered off the hotend within a few seconds.

Is not the same thing?


The real failure case is more subtle, what happens is either the MOSFET Fails in the on position, in which case the firmware can do whatever it wants, the heater will continue getting power. Or more commonly, the thermistor creeps out of the whole so there is no discontinuity in the temperature reading, depending on the repetier algorithm, it MIGHT catch that, but it also might not.

My first melted hotend, the temperature read 190C consistently right up to the point the PEEK melted and the half of the hotend fell onto the bed. The thermistor was loose and slowly worked it's way out as the print progressed, incrementally reading lower and lower relative to actual, the heater just adjusted for the apparent falling temperature, until the hotend literally melted.

Polygonhell
ULTIMATE 3D JEDDI
Posts: 2430
Joined: Mon Mar 26, 2012 1:44 pm
Location: Redmond WA

Re: Kit Mods & Safety & Awesomeness

Postby Polygonhell » Fri Oct 02, 2015 4:26 pm

FWIW I think the JHead guy did some experiments with resettable thermal fuses, it was on his blog, but apparently it's no longer public.
The issue if I remember correctly was finding one that reliably tripped in the desired range without false trips, but the blog post was probably a year plus ago and I might be misremembering.

User avatar
geneb
ULTIMATE 3D JEDDI
Posts: 4742
Joined: Mon Oct 15, 2012 12:47 pm
Location: Graham, WA
Contact:

Re: Kit Mods & Safety & Awesomeness

Postby geneb » Fri Oct 02, 2015 5:26 pm

You were probably talking about Brian Reifsyder's blog. I was discussing this with him today actually. :) A hot end with dual thermistors is a good safe guard against this. He said Marlin has support for it as well. Repetier may as well, but I'm not sure.


g.
Delta Power!
Defeat the Cartesian Agenda!
http://www.f15sim.com - 80-0007, The only one of its kind.
http://geneb.simpits.org - Technical and Simulator Projects

Eric
Printmaster!
Posts: 726
Joined: Sat Aug 18, 2012 4:09 am
Location: Chula Vista, CA

Re: Kit Mods & Safety & Awesomeness

Postby Eric » Fri Oct 02, 2015 6:56 pm

PartDaddy wrote:And, when you are aware of everything, it can still bite you anyway.

Now we have this under control, let's all design Oly's idea for a hot end heated by open flame.


I have a butane-powered soldering iron in my travel toolkit...the concept shouldn't be that hard to adapt to a hot end.

IMBoring25
Printmaster!
Posts: 616
Joined: Wed Mar 18, 2015 1:11 am

Re: Kit Mods & Safety & Awesomeness

Postby IMBoring25 » Sat Oct 03, 2015 1:15 am

Has there been an attempt to code a way to build a profile of a hot end, relating temperature (ideally, temperature difference from ambient), commanded PWM, and a short-duration rolling average of first derivative of temperature? Triggering a fault when the temperature derivative deviates by more than a threshold value from expected should be pretty robust, catching thermistor issues, heater element issues, and even a stuck FET if you give it a relay to kill the machine power.

With addition of a thermal fuse and either a Flame Defender or a fire blanket suspended from low-melting-point fasteners, that would seem to cover just about everything with a fair degree of redundancy.

stonewater
Printmaster!
Posts: 345
Joined: Mon Jan 06, 2014 1:24 am

Re: Kit Mods & Safety & Awesomeness

Postby stonewater » Sat Oct 03, 2015 2:07 pm

oh man I am getting that watchdog auto extinguisher. that is what I have been looking for.

Tom C
MAX V1
325 MM carbon arms trick trucks effector mount LED ring heat spreader
Corvair750
V6 Hotend
Robo 3D
Flashforge creator
http://WWW.TeslagenX.com" onclick="window.open(this.href);return false; - Bedini experimenter kits, books, DVD's

Rob-E
Plasticator
Posts: 9
Joined: Thu Sep 17, 2015 9:53 pm

Re: Kit Mods & Safety & Awesomeness

Postby Rob-E » Tue Oct 13, 2015 4:11 pm

Would it be silly of me to suggest using a heating cartridge and the other hole in the stock hot end to house a thermal fuse and possibly the thermister aswell, or perhaps changing the hole for the thermister from the side of the heating block to the top of the heating block next to heat break shaft so it could be better adhered in place with kapton tape?

User avatar
Eaglezsoar
ULTIMATE 3D JEDDI
Posts: 7185
Joined: Sun Apr 01, 2012 5:26 pm

Re: Kit Mods & Safety & Awesomeness

Postby Eaglezsoar » Tue Oct 13, 2015 4:42 pm

Rob-E wrote:Would it be silly of me to suggest using a heating cartridge and the other hole in the stock hot end to house a thermal fuse and possibly the thermister aswell, or perhaps changing the hole for the thermister from the side of the heating block to the top of the heating block next to heat break shaft so it could be better adhered in place with kapton tape?


Not silly at all!

I have utilized the extra hole to heat my salami but if you have a large salami you will need to find a larger heated hole.

Rob-E
Plasticator
Posts: 9
Joined: Thu Sep 17, 2015 9:53 pm

Re: Kit Mods & Safety & Awesomeness

Postby Rob-E » Tue Oct 13, 2015 5:08 pm

Eaglezsoar wrote:
Rob-E wrote:Would it be silly of me to suggest using a heating cartridge and the other hole in the stock hot end to house a thermal fuse and possibly the thermister aswell, or perhaps changing the hole for the thermister from the side of the heating block to the top of the heating block next to heat break shaft so it could be better adhered in place with kapton tape?


Not silly at all!

I have utilized the extra hole to heat my salami but if you have a large salami you will need to find a larger heated hole.



mm, burnt plastic and salami, sounds delicious

User avatar
626Pilot
ULTIMATE 3D JEDDI
Posts: 1719
Joined: Tue May 14, 2013 12:52 pm

Re: Kit Mods & Safety & Awesomeness

Postby 626Pilot » Tue Oct 13, 2015 8:05 pm

The component that fails more than anything else for me is the thermistor. It happened twice(!!!) on my Budaschnozzle, and it happened a couple of times with various E3Ds. These thermistors may be rated for 280C, but I don't trust them to last forever.

Maybe a screw-in thermocouple, or a thermistor designed for FAR higher temperatures, would be better. I like the way E3D v6 and similar hot ends affix the thermistor, but a screw-in type is probably better.

I think the best solution would be a pair thermal breakers with manual reset (not auto), installed in the chassis, and touching the hot end. They should open above 300C, and they should fail open. They would be wired in series with the switch for the power supply. If either opens, the whole printer shuts down. Alternately, one of the tiny Arduino micros could be wired up to a couple of thermocouples, and that could cut out a normally-open relay if either gets too hot.

BuckeyeVolunteer
Printmaster!
Posts: 44
Joined: Sat Aug 29, 2015 9:04 pm

Re: Kit Mods & Safety & Awesomeness

Postby BuckeyeVolunteer » Tue Oct 27, 2015 8:37 am

I believe a simple thermofuse on the block would be sufficient to prevent thermal runaway. A resetable thermo fuse is a bad idea they can go bad also. I used to work on copiers and they used thermofuses for all the heated components cheap and effective. I think think a complete new look at all the hot ends and how they work. There has to be a better design than what E3d is doing.

Eric
Printmaster!
Posts: 726
Joined: Sat Aug 18, 2012 4:09 am
Location: Chula Vista, CA

Re: Kit Mods & Safety & Awesomeness

Postby Eric » Tue Oct 27, 2015 9:25 am

BuckeyeVolunteer wrote:I believe a simple thermofuse on the block would be sufficient to prevent thermal runaway. A resetable thermo fuse is a bad idea they can go bad also. I used to work on copiers and they used thermofuses for all the heated components cheap and effective. I think think a complete new look at all the hot ends and how they work. There has to be a better design than what E3d is doing.


If fuse reliability is a concern, adding a second fuse at a higher blow temp should cover it. If it blows, you know the other fuse is bad.

enggmaug
Printmaster!
Posts: 305
Joined: Wed Nov 13, 2013 3:54 am
Location: Antony, France

Re: Kit Mods & Safety & Awesomeness

Postby enggmaug » Tue Oct 27, 2015 9:38 am

Reading all this, I believe I will consider adding a thermistance to each hot end, linked to a separate board, like a Teensy, or any arduino like.
This separate monitoring could turn the machine off using a simple relay if the temp reaches a value greater than a given threshold.

That sounds like a quite simple project to develop, and since the hardware is different, the software is different, this independant system in cunjonction with repetier piloting the machine would certainly be safe enough...

I mean, what could happen ? Both boards being faulty at the very same time seems very unlikely... don't you think ?

3D-Print
Printmaster!
Posts: 519
Joined: Mon Jan 05, 2015 9:39 pm
Location: Omaha, Nebraska

Re: Kit Mods & Safety & Awesomeness

Postby 3D-Print » Tue Mar 15, 2016 11:34 am

There have been a couple of comments recently about the "Run-Away Hot -End.

I remembered this thread from last year and thought if it resurfaced it would be good to see if others have advanced their solution and/or approach to avoiding an issue. Maybe something that the masses might employ.
My 3D-Printing learning curve is asymptotic to a Delta's X, Y and Z-axes

IMBoring25
Printmaster!
Posts: 616
Joined: Wed Mar 18, 2015 1:11 am

Re: Kit Mods & Safety & Awesomeness

Postby IMBoring25 » Tue Mar 15, 2016 12:32 pm

enggmaug wrote:Reading all this, I believe I will consider adding a thermistance to each hot end, linked to a separate board, like a Teensy, or any arduino like.
This separate monitoring could turn the machine off using a simple relay if the temp reaches a value greater than a given threshold.

That sounds like a quite simple project to develop, and since the hardware is different, the software is different, this independant system in cunjonction with repetier piloting the machine would certainly be safe enough...

I mean, what could happen ? Both boards being faulty at the very same time seems very unlikely... don't you think ?


You'd need to design the hardware so the redundant thermistor is unlikely to fail at the same time as the primary one and the firmware so it would also recognize shorts and disconnects.

RegB
Printmaster!
Posts: 292
Joined: Fri Jun 27, 2014 7:45 pm

Re: Kit Mods & Safety & Awesomeness

Postby RegB » Wed Oct 03, 2018 2:02 pm

An old thread, I know - and I don't know WHY it is that I didn't jump on it YEARS ago...

Anyway, there are fail safe design principles (like Duhh, we knew that already) and for such potential problems as thermal runaway it oesn't seem HARD to implement a design rule along the lines of;

Allow power to this section ONLY while there is definite feedback that the temperature is BELOW some threshold (say 20 above the desired temp).
(REQUIRE the definite feedback)

Instead of of the all too easy;
Allow power to this section, apply power until there is feedback saying that it is too hot.


Return to “General Announcments”

Who is online

Users browsing this forum: No registered users and 1 guest